The present invention relates to a transportation method and transportation apparatus using a transport robot for transporting between processing steps substrate wafers used, for example, in semiconductor integrated circuits, liquid crystal displays panels, solar battery panels.
This application is based on patent application No. Hei 8-315193 filed in Japan, the content of which is incorporated herein by reference.
Semiconductor elements such as semiconductor integrated circuits and semiconductor lasers, active matrix type liquid crystal display panels, solar battery panels, etc., are manufactured by a process of laminating in sequence various predetermined thin films on a silicon substrate, gallium arsenide substrate, glass substrate, etc. whose surfaces are highly cleaned. An extremely high degree of precision is required in the manufacture of each of these products, and if only a slight amount of impurity adheres to or is absorbed by the surface of the processed substrates, that is, the substrate wafer, it is difficult to manufacture a high quality product. In addition, during transportation or in the course of each type of processing, these substrate wafers can acquire static electricity, and as a result, it is easy for impurities to be attracted to or adhere to them.
For example, if water, an impurity such as moisture, is absorbed by the surface of a semiconductor substrate during a manufacturing step, it will cause a hindrance to the manufacturing step. Furthermore, if the amount of water is large, a natural oxide film will generate on the film surface if there is oxygen in the atmosphere. In addition, in the manufacturing steps of the thin film transistor (TFT) used in liquid crystal panels, if there is water on the surface of the insulating film made, for example, of SiNx, it is impossible to precisely form an amolphous silicon (a-Si) film with uniform thickness on top of it. Additionally, the process of fabricating gate oxide film in the manufacturing integrated circuits (IC), if there is water on an n- or p-region surface, an SiOx film will form at the interface between the SiO2 and Si, and the MOS transistor will not function as a switch. Similarly, if there is water on the surface of a capacitor, an SiOx film will form in its interface making it impossible to charge the capacitor electrode, and it will not function as a memory device.
In addition, in order to prevent spiking due to tungsten silicide in the wiring process, a TiN film is formed before depositing a tungsten (W) film, but if there is water on the substrate, problems such as the deterioration of the adhesiveness of the TiN film occur.
Furthermore, when there are impurities other then water, for example, organic impurities such as methane, during heat processing, the silicon reacts with the carbon on the surface of the substrate (silicon), forming an SiC film, and problems are caused in the operating characteristics of the device.
Usually, each type of processing apparatus used in the manufacture of semiconductor integrated circuits, etc., are disposed in a clean room from which particulate matter has been filtered. Because semiconductor integrated circuits, etc, are manufactured by many processing steps, in order to carry out the operation of each step, the work (the substrate wafer) is transported from one processing apparatus to the processing apparatus of the next step. In order to do this, the substrate wafer is exposed to the air in the clean room at the time of transportation.
The interior of a clean room is usually maintained at a temperature of 20xcx9c25xc2x0 C. and at a relative humidity of about 50%, and the gaseous impurities of the excluded particles may exist in abundance. Because of this, the impurities that exist in the atmosphere of the clean room are absorbed by the surface of the substrate wafer. For example, water can be instantaneously absorbed by the surface of the substrate wafer. When trying to prevent the absorption of this water, it is in fact, however, extremely difficult to exclude water from the entire clean room.
Thus, a transportation system in which substrate wafers are transferred from one processing apparatus to the next processing apparatus in an inert gas atmosphere using a special transport robot transporting substrate wafers is proposed.
The transportation robot in this case is provided with a storage box (storage chamber) which can store substrate wafers in an inert gas atmosphere. In addition, on the processing apparatuses which carry out operations of each step, a transportation chamber to which substrate wafers can be delivered in the inert gas atmosphere is provided as an accessory.
In this transportation system, by activating a transportation robot, the substrate wafers stored in the inert gas atmosphere in the storage box are transported from the transportation chamber of one step to the transportation chamber of the next step. Additionally, at the stage where the transportation robot has arrived in front of the transportation chamber, the storage box of the transportation robot and the transportation chamber are connected, and there respective gates are opened, and between the storage box and the transportation chamber, the delivery of the substrate wafer occurs. For example, the substrate wafers are brought into the transportation chamber from the storage box, these substrate wafers are transferred from the transportation chamber to the processing apparatus, and a predetermined processing is carried out. When the processing is finished, the substrate wafers are returned to the transportation chamber, and again returned to the storage box. Finally, the gates are closed, and the substrate wafers are transported to the next step by activating the transportation robot.
However, delivering the substrate wafers between the storage box of the transportation robot and the transportation chamber of the processing apparatus is carried out via a gate valve installed in each gate of the storage box and the_ transportation chamber, and the front surface of the gate valve having a concave part is structurally unavoidable. Because of this, the air in the clear room collects in this concavity, and as a result, the problem arises that when placing or removing the substrate wafers, simultaneously the air collected in this concavity becomes mixed into the transportation chamber and the storage box. Therefore, even if the interior of the storage box, transportation chamber, or processing apparatuses are maintained with an highly cleaned atmosphere having almost no particles, water, gaseous impurities, etc., when placing and removing the substrate wafers, mixing with a small amount of air cannot be avoided, and causing a deterioration in each processes carried out on the substrate wafers.
In addition, when the substrate wafers are stored in the storage box and transported to the next process, in order to preserve the highly cleaned atmosphere of the storage box, a container (cylinder) filled with highly pure inert gas is maintained in the transportation robot. In addition, because impurities in the storage box are not monitored, a gas flow always larger than the necessary amount is ventilated from this container. As a result, the problem arises that the container is enlarged, and the transportation robot itself must become large. In order to miniaturize the container, when the amount of the gas flow was decreased, the problem arises that it becomes very difficult to maintain the highly pure atmosphere.
The object of the present invention is to provide a transportation method and a transportation means which can prevent mixing of air which accumulates in the concavity in the front surface of the gate valve when the substrate wafer is transported from one process to the next process by a transportation robot provided with a storage box.
The transportation method for substrate wafers of the present invention is characterized as a method in which substrate wafers are transported between transportation chambers attached to processing apparatus and containing an inert gas atmosphere using a transportation robot provided with a storage chamber which can store a substrate wafer in an atmosphere of inert gas, and during placement and removal of the substrate wafer between the storage chamber of said transportation robot and the transportation chamber of the processing apparatus, disposing a connection chamber between the storage chamber and the transportation chamber, and after introducing the inert gas into said connection chamber at low pressure, opening the gate of the storage chamber and the transportation chamber, and placing or removing the substrate wafer.
In this transportation method of substrate wafers, the above inert gas is measured at a semiconductor laser detector, and from the result the ratio of impurities in the chambers is calculated, and it is preferable that the amount of inert gas introduced in each chamber and the placement and removal operation for the substrate wafer be controlled based on this data.
Furthermore, in the transportation method for substrate wafers of the present invention, the preferred structure is that wherein if the volume of said storage chamber, transportation chamber, and connecting chamber are respectively V1 [cm3], V2 [cm3], and V3 [cm3], respectively, and the impurity ratios are xcex31, xcex32, and xcex33, respectively, when the total area of said substrate wafer is S [cm2], then when: 2.7xc3x971019 [molecules/cm3]xc3x97(V1xc3x97xcex31+V2xc3x97xcex32+V3xc3x97xcex33)xe2x89xa61013 [molecules/cm2]xc3x97S is satisfied, said substrate wafer is placed in or removed from between said storage chamber and said transportation chamber.
In the transportation method of substrate wafers of the present invention, in place of the above-mentioned inert gas, it is possible to use a mixed gas comprising an inert gas and oxygen gas.
In addition, the transportation apparatus for substrate wafers of the present invention is characterized in having a sealed transportation chamber attached to a processing apparatus for a substrate wafer, providing a placement and removal opening for placing and removing the substrate wafer between the outside of said transportation chamber, providing a gate valve on this placement and removal opening which seals this placement and removal opening, and on a transportation robot which can move between transportation chambers providing a sealed storage chamber which stores the substrate wafer, providing a placement and removal opening for placing and removing substrate wafers between the outer part of the storage chamber, providing a gate valve on this placement and removal opening which seals this placement and removal opening, and by opening the gate valve when the storage chamber and transportation chamber are connected, in the transportation apparatus of the substrate wafer which places and removed the substrate wafer, providing a sealed connection chamber interposed between this storage chamber and transportation chamber, and providing a gas intake opening and an exhaust opening for ventilating inert gas to the storage chamber, transportation chamber, and connection chamber, a vacuum exhaust means for ventilating at low pressure.
In this transportation apparatus, it is preferable that the structure be provided with a semiconductor laser detector which measures the concentration of impurities in each chamber, and a control means which calculates the ratio of impurities in each chamber from the concentration of impurities, and controls the placing and removing of substrate wafers between the storage chamber and the transportation chamber based on this calculation.
In the transportation apparatus for substrate wafers, in place of the above-mentioned inert gas, a mixture of inert gas and oxygen gas can also be used.